Strip shingles of the known type include certain random butt edge features which impart a desirable aesthetic appeal to a roof covered with a plurality of such shingles. One example of such a strip shingle is shown in U.S. Pat. No. 2,205,679. This patent shows a composition shingle having a distinctive butt edge comprised of seven linear butt edge features. Each of these butt edge features is set apart from adjacent butt edge features by differing in vertical height or slope from that of adjacent butt edge features.
Illustrating the tab shingle which includes vertical slot cutouts defining a plurality of tabs in each shingle is U.S. Pat. No. 2,348,223. This patent discloses a classic three-tab shingle. Each of the tabs is of substantially equal length, this length being defined by the two vertically extending slot cutouts which divide the shingle into the three tabs. Of particular note is the use of the vertical slot cutouts to aid in positioning each subsequent course of shingles relative to one another on a roof deck. The butt edge of shingles in each subsequent course is aligned so as to be tangent to the upper end of each slot cutout. This alignment assures a uniform degree of exposure of each tab on the roof deck. Also, the slot cutouts permit the workman to apply the shingle with substantially uniform alignment offset wherein the slot cutout of shingles in a subsequent course is positioned so as to bisect the tabs of the immediately preceding course. This alignment offset produces a pleasing aesthetic effect and breaks up the vertical pattern which would be created if each slot cutout were aligned with the just preceding slot cutout. Also, by offsetting the cutouts there is a reduced chance of leakage of for example wind-driven rain passing through one slot cutout to the juncture between the headlap portions of adjacent shingles in the immediately preceding course of shingles.
A composition shingle having features of a tab shingle, as well as having a nonuniform or random butt edge configuration, is illustrated by U.S. Pat. No. 2,199,760. The shingle disclosed therein has a series of butt edge features separated by slot cutouts, these cutouts being spaced at random distances along the length of the shingle. The tabs defined by these cutouts has a butt edge portion varying in length, width and contour. In the case of another embodiment, the tabs vary in length as well as mineral granule coloration, at least along the lower fraction of the butt portion. On this shingle certain alignment aids are provided on the sides or edges of the headlap portion thereof. The alignment feature comprises a finger-like protrusion on the leading edge at the headlap portion and a corresponding, negatively shaped slot or indentation on the trailing edge. These protrusions and slots are provided by a known manner at the time the shingles are cut from a continuous roll of composition material. Also, along the upper edge of the shingle (and hence the upper edge of the headlap portion) there is a triangular shaped notch defining the longitudinal center of the shingle. When shingles of this type are applied to a roof deck, the protrusion on the leading edge and the indentation on the trailing edge are aligned with the upper edge of the shingle in the immediately preceding course of shingles. This vertical alignment provides proper and uniform exposure of the random tabs of the shingle. Proper alignment offset of the shingles relative to the immediately preceding course of shingles is assured by aligning the leading edge, for example, with the triangular shaped notch on the upper edge of the subjacent shingle in the immediately preceding course of shingles. Each subsequent shingle in the course of shingles being applied is aligned with the immediately preceding shingle by inserting the finger-like protrusion in the leading edge thereof into the indentation of the trailing edge of the immediately preceding shingle.
Another rectangular shingle known to Applicant, and marketed by Johns-Manville Corporation under the Trademark RAMPART, has a butt edge configuration similar to that of the shingle illustrated in U.S. Pat. No. 2,205,679, and utilizes a stepped leading and trailing edge to provide indicia for proper and consistent exposure. In this alignment system, the leading edge of each shingle consists of two linear portions offset from one another by a quarter-inch step. This step occurs about five inches from the top edge of the shingle. The trailing edge comprises a similar configuration but wherein the quarter-inch step defines a notch along the top five inches of the trailing edge. The step in the leading edge fits into the notch on the trailing edge of the next succeeding shingle.
U.S. Pat. No. 3,919,823 discloses a strip shingle with a butt edge configuration simulating the appearance of wood shingles. A knife slit provided to the right of the leftmost butt edge feature permits the thus defined overlap tab to be placed over the trailing edge of the just preceding shingle in the course of shingles. This creates a double thick butt portion. Conventional alignment features are provided along the leading and trailing edges of the disclosed shingle.
Thus, the prior art shingles comprised two apparently mutually exclusive alignment concepts. In the case of a random butt edge featured shingle, alignment features in or on the edges of the headlap portion were required in order to assure a proper, aesthetically pleasing and properly functioning shingled roof. A tab shingle, having uniform butt edge features, utilized the slot cutouts and the uniform and predictable butt edge to assure proper and uniform exposure. However, in certain critical applications, even the tab shingle required indicia in the headlap portion to assure precise alignment offset.